Low cost and fast method to massively produce graphene and graphene oxide with carbon-rich natural materials and the use of the same

ABSTRACT

This invention provides an innovative method to manufacture graphene layers or quantities and graphene oxide layers or quantities from graphite, coal slags, asphalt, and other carbon-rich sold materials in nature. The present invention uses controllable microwave irradiation to heat the mixtures of basic material, graphite, or coal slags, or asphalt, or their combinations with ionic liquids and surfactant plus environmentally friendly oxidation agents. This invention can generate the said-products of graphene layers and graphene oxides in a short time period of one second to 300 seconds. The present invention does not involve any concentrated sulfuric acid, nitric acid, nor huge water quantities needed for the purification, unlike the prior art. The as-produced graphene-based materials can be used for preparing conductive films for touch screens, producing graphene carbon fibers and three-dimensional porous graphene nanomaterials, and preparing graphene-based other intelligent nanocomposites for super-light-weight machines and vehicles.

FIELD OF THE INVENTION

The present invention is mostly related to an innovative technology toproduce massive graphene layers and graphene oxide layers from previousreported methods for different applications. It also provides a newexciting application of carbon rich solid waste such as coal slags andasphalt for advanced graphene nanomaterials for society.

BACKGROUND

In the entire graphene field, the traditional and famous Hummer's methodhas been so widely used to synthesize graphene layers and grapheneoxides in laboratories and many industrial companies forcommercialization. However, it has caused reactor explosions due tolarge amount of heat and gases released, because the use of strong acidssuch as nitric acid, sulfuric acid, and strong oxidation agents such asKMnO₄, P₂O₅, K₂S₂O₈ and so on. Purification of the products normallyneed to use centrifuge and have to use large amounts of water to washaway the strong acids from the graphene products. Thus, strong acids arewaste products in this process. In addition, the reaction time needsover at least one day. It is an extensive time consuming and energy-highdemanded method that we have to overcome. A number of other methods havebeen reported to try to substitute the Hummer Method from differentresearch groups, such as electrochemical exfoliation, potassium ferratereplacing KMnO₄ for one step oxidation in sulfuric acid, andmicrowave-irradiation assistant in ionic liquids. They either stillsuffer time consuming and waste-acid producing problem, centrifugepurification facility high cost, or expensive raw materials of ionicliquid materials bottleneck problems for commercialization.

To overcome the significant pollution, high energy-demand, andtime-consumption problems that are factors in the conventional grapheneproduction methods, our present invention provides an innovativetechnology in using carbon rich solid materials from nature combinedwith certain low cost additives and microwave irradiation to quickly andgreen-chemically produce massive graphene layers and graphene oxides fordifferent applications without involving strong acids, without needcentrifuge technology, and without large quantities of water. Processingtime is in the seconds to minutes range, which can dramatically decreasethe manufacturing cost.

SUMMARY OF THE INVENTION

The present invention uses graphite, coal slags, asphalt, and othercarbon-rich sold materials in nature. It generally uses controllablemicrowave irradiation to heat the mixtures of a base (“basic material”),graphite, or coal slags, or asphalt, or their combinations with ionicliquids and surfactant plus environmentally friendly oxidation agents.This invention can generate the said-products of graphene layers andgraphene oxides from a short time range of, for example, approximately 1second to 60 min. It does not involve any concentrated sulfuric acid,nitric acid, nor are huge quantities of water needed for thepurification. The as-produced graphene-based materials can be used, byway of non-limiting example, for continuously preparing conductive filmsfor touch screens, cost- effectively producing graphene carbon fibersand three-dimensional porous graphene nanomaterials, and preparinggraphene-based intelligent nanocomposites for super-light-weightmachines and vehicles. There are many more potential applications thatmay be explored gradually by this invention.

The present invention represents an opportunity to provide low cost,energy savings, greener chemical process manufacturing for advancedgraphene and its based-nanomaterials, as well as for graphene oxide andits based nanomateirals for different applications. It works by one stepto form high quality graphene layers and graphene oxide layers and theircombinations.

The purpose of the invention is to provide a method to manufacturegraphene and graphene oxide layers from one to a few layers rangemanufacturing process.

Another purpose of the invention is to provide large amounts of wasteusage method for coal slags and asphalt.

A further purpose of the invention is to allow for the industrymanufacturing of graphene and graphene oxides in one step usingmicrowave reactors only, which does not have as much waste and pollutionreleased to the environment as current methods do.

Another purpose of the invention is to significantly decrease therequired manufacturing time to produce the designed products.

A further purpose of the invention is to decrease the requirements ofequipment for the manufacture of massive graphene and graphene oxidefrom all kind of graphite including normal graphite and expandablegraphite, and even impurities-contained graphite, impurities-containedcoal slags, or impurities-contained- asphalt. Thus the carbon rich solidraw materials can be broadened significantly. It is not necessary tohave 99.0% purity of the graphite and the coals or asphalt.

Another purpose of the invention is to produce graphene layers andgraphene oxide layers that may be functionalized directly during themicrowave irradiated reactions with the addition of other elements suchand/or compositions which can be used to create products which have abroad range of unique and enhanced functional properties, such asnitrogen doping, thermo-conductivity and electrical conductivitymanagement and adjusting, resistance to corrosion, and many otherproperties that will be able to be used to improve electronics, energyefficiency, solar water splitting for hydrogen fuel, better batteryelectrode materials design, and formation of molecules similar topolyacrylonitrile (PAN) for high quality graphene-based carbon fiberproduction etc.

A further purpose of the invention is to reduce the environmental impactand reliance on energy-saving and green chemical manufacturing.

BRIEF DESCRIPTION OF THE DRAWING

The utility method shall be hereby described in detail in thedescription with reference to the attached drawing, in which:

FIG. 1 is a flowchart showing a method of manufacturing graphene andgraphene oxide through microwave irradiations using carbon rich solidmaterials such as graphite, coal slags, and asphalt etc.

FIG. 2 provides a photograph of an embodiment of the present invention.

FIG. 3A shows an EDAX analysis of graphene layers obtained fromMicrowave Processing.

FIG. 3B shows an EDAX analysis of graphene layers obtained fromMicrowave Processing.

FIG. 4A shows a Raman spectroscopy characterization of graphene oxideproduced directly from the microwave processing.

FIG. 4B shows the characterization of atomic force microscope image andit shows the graphene oxide flakes consisting of 2 to 5 layers directlyobtained in this invention.

DETAILED DESCRIPTION OF THE INVENTION

The aforementioned goals are achieved by the present invention usingmicrowave reactor such as a magnetron-based microwave devices to providecontrollable irradiation to substance mixture that is formed uniformlyby carbon rich solid raw materials such as graphite, coal slags,asphalt, a basic material, surfactants, and small amount of ionic liquidsolvent, as well as small amounts of optional additives. The microwavemay be capable of providing microwave energy having an intensity ofabout 150 to about 3000 W. The microwave irradiation time is in secondsand minutes from 1 second to 60 min varied with different type of carbonrich solid materials. Pretreatment to ensure the mixture to be uniformin some cases is needed, such as grinding-milling graphite with a basicmaterial, and surfactants, and ionic liquid. Posttreatment to theas-prepared graphene layers or graphene oxide layers will be performedeasily by adding the primary products into water and useultra-sonication to disperse the mixture to uniform suspension, thenflowing selection to the graphene layers or graphene oxide layers willbe carried out by flowing out the suspension in different verticalheight levels.

Examples of carbon rich solid raw materials include, but are not limitedto graphite, acid-treated expandable graphite from different suppliers,all kinds of coal slags such as brown coal slags, and asphalt fromre-fining oil plants.

Examples of basic materials include, but are not limited to sodiumhydroxide, potassium hydroxide, baking soda, sodium bicarbonate, urea,ammonium hydroxide, and all salts that can be dissolved in water whilemaintaining pH value higher than 6.

Examples of surfactants include, but are not limited to all cations andionic surfactants, such as quaternary ammonium salts, cetrimoniumbromide, polyatomic cations such as poly(diallyldimethylammoniumchloride) (PDDA), organic ammonium cation, iminium salt, polystyrenesulfonates etc.

Examples of ionic liquid solvents include, but are not limited to ionicliquids, such as all salts of imidazolium, pyridinium salts,1-butyl-3-methylimidazolium (BMIM)-based and 1-ethyl-3-methylimidazolium(EMIM)-based ionic liquid, such as 1-ethyl-3-methylimidazoliumtetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, butpreferring acetate salts for environmental consideration. In some cases,water, alcohols, acetone, ketones, dimethyl formamide (DMF), ethyleneglycol (EG), DMSO, and their co-solvents, but generally prefer ionicliquids, water, and alcohols for the green chemical manufacturing.

Examples of additional additives include, but are not limited toazodicarbonamide, small molecules amines, ammonium hydroxide, urea,metal oxides (MgO, ZnO, Fe₃O₄, Co₂O₃, NiO, ZrO₂, or MoS₂, WS₂, Al₂O₃, ortheir combination), and metal nanoparticles (Ni, Fe, Co, Mg, Al, steelalloy nanopowder, Pd, or their combinations) may be used to ensure aspecially functionalization to graphene and graphene oxide during thereactions. Also, additional additives may be oxidation reagents for somecase reactions to realize graphene oxide layers obtained. The additivescan be, but are not limited to, KMnO₄, potassium ferrate, sodiumferrate, peroxide. For safety and environmental consideration,preferring potassium ferrate, sodium ferrate, hydrogen peroxide as needfor some case reactions.

The as-prepared graphene layers in slurries may be directly conductedwith additives to massively manufacture graphene-based carbon fibers, orto prepare graphene-based nanocomposite functional films, or tosynthesize three dimensional porous graphene based nanocomposites fordifferent applications, or to conduct 3D additive printing manufacturingfor parts or articles for automobiles and machines including roboticsand airplanes and ships, among other applications.

In summary, our invention leads to large a number of graphene layers andgraphene oxide layers produced in microwave reactor in a few minutes andin a one step reaction without using any strong acid and without largeamounts of water. The as-prepared products have excellent mechanicalproperties such as strength, and adjustable properties for thermal andelectrical conductivities, shielding radiations, and electromagneticwaves, anti-corrosion, and more.

Referring to FIG. 1, showing the operational flowchart of the method ofmanufacturing graphene and graphene oxides according to the presentinvention. As shown in FIG. 1, the method of the present inventiongenerally comprises the steps of obtaining graphite, coal slags, orasphalt S10, mixing with the said solvent(s), surfactant(s), additive(s)that includes oxidation reagents under grinding-milling S20, andconducting the mixed suspension into a properly designed MicrowaveReactor applying an irradiation with intensity between 150 W to 3000 W,and S30 time between 1 second to 60 minutes, preferring 500 W and lessthan 10 minutes for pre-treated graphites and asphalt, but 500-1500 Wand within 30 min for coal slags. Mixing may be achieved by anultrasonic mixer, grind milling, and any other process. By altering theirradiation treatment applied, the qualities of the resulting grapheneand graphene oxide can be manipulated and enhanced; finally graphene andgraphene oxide slurry is prepared by simply separating the as-preparedgraphene/graphene oxide layers with solvents S40.

Examples of this invention are given as follows:

FIGS. 2 and 3 gives the photo of this invention that shows the microwaveirradiation and the dispersed graphene or graphene oxide suspensions forfloating selection for different applications. FIG. 2 shows microwaveirradiation and the dispersed graphene or graphene oxide suspensions forfloating selection for different applications.

To obtain graphene oxide layers, oxidation agents and correspondingadditives are different from graphene layer exfoliation. Pretreatment isnecessary before microwave irradiation.

1) Graphene few layers product:

Normal graphite can be used as graphene source. In FIG. 1, during thegrind-milling process, additives added into graphite are mostly ioniccompound(s) plus surfactant and iron or cobalt or nickel salt. Microwaveirradiation for graphene productions should be for a shorter time thanfor generation of graphene oxide. For instance, irradiation time ispreferred in the range of 1 second to 3 min. To avoid an accident fromoverheating or sparking for a safe process, aluminum hydroxide,magnesium hydroxide, or phosphoric acid or phosphorus salts can be addedwith a concentration 0.01% to 20% to the mixture, preferably around˜10%. A suspension is obtained after directly dispersing the microwaveirradiated mixture. Graphene layers are floating on the water. Thefloating graphene can be directly separated by filtration and used forconductive films, radiation absorption films, or graphene powderpreparation for graphene composites, for instance to preparepolymer-graphene compounds for nanofibers. In FIG. 2 on the right is thephoto of the invention floating selection for graphene few layersproduct. This product shows high conductivity and easily disperse in DMFor other organic solvents for conductive products manufacturing.

2) For graphene oxide few layer products

Expandable graphite in the market can be used as graphene oxide source.In FIG. 1, during the grind-milling process, additives added intographite are mostly ionic compound(s) plus surfactant and oxidationagent with iron or cobalt or nickel salt. Microwave irradiation shouldbe for a longer time than the generation of graphene layers. Forinstance, the microwave irradiation time is preferably in the range of 1min to 30 min. To avoid accident from overheating or sparking for a safeprocess, aluminum hydroxide, magnesium hydroxide, or phosphoric acid orphosphorus salts can be added with a concentration 0.01% to 20% themixture, with preferably around ˜10%. A suspension is obtained afterdirectly dispersing the microwave irradiated mixture in water. Grapheneoxide layers are floating on the water, which can be directly separatedby filtration and used for graphene-based carbon fiber manufacturing, or3D printed graphene machine articles. The lower level graphene oxide inthe suspension at the bottom of the container, having higher oxygen tocarbon ratio than that of the upper suspension, can be used for porousgraphene oxide foam and radiation absorption films, or graphene powderpreparation. FIG. 2 on the left is the photo of the invention floatingselection for graphene oxide layers' products. This product shows someconductivity and easily disperses in polar organic solvents (methanol,alcohol, isopropyl alcohol, DMF, and water etc. It can be directly usedfor graphene carbon fiber manufacturing, and produce multifunctionalgraphene nanomaterials for energy-related applications.

FIG. 3A shows the graphene product obtained from this invention usinggraphite as the natural raw materials, which consists of 1 to 4 layersin the suspension, and FIG. 3B shows its high pure quality over 95%carbon in wt as indicated in EDAX analysis. Raman spectroscopy confirmsthe high quality of graphene layers. FIG. 4A is the Raman spectroscopycharacterization of graphene oxide produced directly from the microwaveprocessing.

FIG. 4B is the characterization of atomic force microscope image and itshows the graphene oxide flakes consisting of 2 to 5 layers directlyobtained in this invention, indicating a high quality manufacturing fora massive graphene oxide product.

The grind-milling agents for coal slags or petroleum asphalt will bebasic, such as sodium hydroxide, calcium hydroxide and ionic compoundplus some salt in this invention. To produce graphene based on the coalor petroleum asphalt would be similar to the graphite processing, withthe difference of the irradiation time and microwave power as indicatedin previous description.

Additionally, for coal slags and petroleum asphalt carbon rich naturematerials, the grind-milling agents are basic, such as sodium hydroxide,calcium hydroxide and ionic compound plus some salt in this invention.To produce graphene few layers based on the coal or petroleum asphaltwould be similar to the graphite processing, with the difference of theirradiation time and microwave power as indicated in previousdescription.

What is claimed is:
 1. A method for producing at least one of grapheneand graphene oxide comprising the steps of: mixing a carbon richmaterial with a solvent, forming a mixture; directing a sufficientquantity of microwave radiation to the mixture to form at least one of aquantity of graphene and a quantity of graphene oxide; and separatingthe at least one of the formed quantity of graphene and quantity ofgraphene oxide from the solvent.
 2. The method of claim 1 wherein themixture further comprises a surfactant.
 3. The method of claim 1 whereinthe mixture further comprises an additive.
 4. The method of claim 2wherein the mixture further comprises an additive.
 5. The method ofclaim 4 further comprising the step of conducting the mixture into amicrowave reactor, the microwave reactor configured to provide microwaveradiation to the mixture, the directing step occurring in the microwavereactor.
 6. The method of claim 1 wherein the step of directing forms aquantity of graphene.
 7. The method of claim 1 wherein the step ofdirecting forms a quantity of graphene oxide.
 8. The method of claim 1wherein the directing step comprises directing microwave radiationhaving an intensity of 150 W to 3000 W.
 9. The method of claim 1 whereinthe step of directing the microwave radiation to the mixture isperformed for a time period of between approximately 1 second andapproximately 60 minutes.
 10. The method of claim 1 wherein the carbonrich material is at least one of graphite, acid-treated expandablegraphite, coal slags, brown coal slags, and asphalt.
 11. The method ofclaim 1 further comprising the step of adding a basic material to themixture before or after the mixing step, wherein the basic material isat least one of sodium hydroxide, potassium hydroxide, baking soda,sodium bicarbonate, urea, ammonium hydroxide, and salts that can bedissolved in water while maintaining pH value higher than
 6. 12. Themethod of claim 2 wherein the surfactant is at least one of quaternaryammonium salts, cetrimonium bromide, polyatomic cations such aspoly(diallyldimethylammonium chloride) (PDDA), organic ammonium cation,iminium salt, and polystyrene sulfonates.
 13. The method of claim 1wherein the solvent is at least one of salts of imidazolium, pyridiniumsalts, 1-butyl-3-methylimidazolium (BMIM)-based and1-ethyl-3-methylimidazolium (EMIM)-based ionic liquid, such as1-ethyl-3-methylimidazolium tetrafluoroborate,1-butyl-3-methylimidazolium hexafluorophosphate, water, an alcohol,acetone, a ketone, dimethyl formamide (DMF), ethylene glycol (EG), DMSO,and their co-solvents.
 14. The method of claim 3 wherein the additive isat least one of azodicarbonamide, a small molecules amine, ammoniumhydroxide, urea, metal oxides, metal nanoparticles, KMnO4, potassiumferrate, sodium ferrate, and peroxide.
 15. The method of claim 1 whereinthe step of mixing comprises grind-milling.
 16. The method of claim 1wherein the step of mixing comprises mixing with an ultrasonic mixer,the mixing with the ultrasonic mixer creating a mixture having asubstantially uniform suspension.
 17. The method of claim 1 furthercomprising the step of grinding the carbon rich material before themixing step.
 18. The method of claim 1 further comprising the step offorming carbon fibers from the at least one of the separated grapheneand graphene oxide.
 19. The method of claim 1 wherein the directing stepcomprises directing microwave radiation having an intensity ofapproximately 1500 W.
 20. The method of claim 1 wherein the step ofseparating the formed graphene and graphene oxide from the solventcomprises draining the components from the microwave reactor into aquantity of water, the water allowing the formed graphene and grapheneoxide to separate from the solvent.